The present invention relates to a process and apparatus for electrical discharge machining a workpiece by means of an electrode tool in the form of a wire, consecutive voltage pulses being applied between the electrodes such as to trigger the electrical discharges.
In travelling wire EDM apparatus, the electrode wire and workpiece and displaced relative to each other such as to effectuate a cut through the workpiece according to a programmed path. It is convenient to supply the machining current to the machining zone between the electrode wire and the workpiece on both sides of the machining zone by means of two electrical connections each comprising a contact in engagement with the electrode wire connected to one of the terminals of the EDM pulse generators, the other terminal of the pulse generator being connected to the workpiece to be machined.
As long as electrical discharge machining is effected in a normal manner, the electrical discharges across the machining gap between the electrodes occur entirely at random. However, it has been observed that concentration of the electrical discharges may occur at a particular point of the machining zone, with the result that normal machining is disturbed and the number of abnormal electrical discharges is increased, which may cause rupture of the electrode wire due to localized excessive heating of the electrode wire. Disturbance of normal machining conditions can be avoided by rapidly modifying some of the machining parameters such as the energy of the electrical discharges, or the flow rate of the machining fluid. It is consequently advantageous to detect a localized concentration of electrical discharges in order to prevent abnormal machining.